Method of fabricating and/or repairing a light emitting device

ABSTRACT

A method of repairing a light emitting device which makes high quality image display possible even if a pin hole is formed during formation of an EL layer is provided. The method of repairing a light emitting device is characterized in that a reverse bias voltage is applied to an EL element at given time intervals to thereby reduce a current flowing into an EL element when the reverse bias voltage is applied to the EL element.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of fabricating and/orrepairing an electroluminescence (EL) panel in which anelectroluminescence (EL) element formed on a substrate is sealed betweenthe substrate and a cover member. The Invention also relates to a methodof repairing an EL module obtained by mounting an IC to the EL panel.The EL panel and the EL module are generically called light emittingdevices in this specification.

[0003] 2. Description of the Related Art

[0004] Being self-luminous, EL elements eliminate the need for abacklight that is necessary in liquid crystal display devices (LCDs) andthus make it easy to manufacture thinner displays. Also, theself-luminous EL elements are high in visibility and have no limit interms of viewing angle. These are the reasons for attention that lightemitting devices using the EL elements are receiving in recent years aselectro-optical devices to replace CRTs and LCDs.

[0005] An EL element has a layer containing an organic compound thatprovides luminescence (electroluminescence) when an electric field isapplied (the layer is hereinafter referred to as EL layer), in additionto a cathode layer and an anode layer. Luminescence obtained fromorganic compounds is classified into light emission upon return to abase state from singlet excitation (fluorescence) and light emissionupon return to a base state from triplet excitation (phosphorescence).The repairing method of the present invention is applicable to a lightemitting device whichever light emission the device uses.

[0006] All the layers that are provided between an anode and a cathodeare an EL layer in this specification. Specifically, the EL layerincludes a light emitting layer, a hole injection layer, an electroninjection layer, a hole transporting layer, an electron transportinglayer, etc. A basic structure of an EL element is a laminate of ananode, a light emitting layer, and a cathode layered in this order. Thebasic structure can be modified into a laminate of an anode, a holeinjection layer, a light emitting layer, and a cathode layered in thisorder, or a laminate of an anode, a hole injection layer, a lightemitting layer, an electron transporting layer, and a cathode layered inthis order.

[0007] In this specification, an EL element emitting light is expressedas an EL element being driven. The EL element as defined herein is alight emitting element comprising an anode, an EL layer, and a cathode.

[0008] In general, an EL element is fabricated by forming one ofelectrodes, namely, an anode or a cathode, then forming an EL layer soas to contact the electrode, and lastly forming the other electrode, acathode or an anode, so as to contact the EL layer.

[0009] The EL layer is formed mainly by evaporation or spin coating.With either method, manufacturers take trouble to wash a substratebefore forming the EL layer and the electrodes, throughly monitor thecleanliness in a clean room where the film formation takes place, andthe like.

[0010] Despite those efforts, sometimes dusts land on the electrodes orother portions to open a hole (pin hole) in the formed EL layer. FIG.12A shows a simplified sectional view of an EL element 200 in which twoelectrodes 201 and 202 short-circuit. If there is a pin hole formed inan EL layer 203, the two electrodes 201 and 202 can be connected to eachother in the pin hole to short-circuit when the electrode 202 is formedon the EL layer 203. Hereinafter, a portion having a pin hole where twolayers sandwiching a light emitting layer are connected to each other iscalled a defect portion 204.

[0011]FIG. 13A shows the voltage-current characteristic of an EL elementthat has no defect portion whereas FIG. 13B shows the voltage-currentcharacteristic of an EL element that suffers from short circuit at adefect portion.

[0012] Comparing FIGS. 13A and 13B, the amount of current flowing in theEL element 200 when a reverse bias voltage is applied to the EL element200 is larger in the case of FIG. 13B.

[0013] This is because two electrodes short-circuit in the defectportion 204 in the case of FIG. 13B unlike that of FIG. 13A and acurrent flows through the defect portion 204.

[0014] Short circuit of the two electrodes 201 and 202 taking place inthe defect portion 204 reduces the luminance of light emitted from theEL layer. The current flow when a forward bias voltage is applied to theEL element having the defect portion is schematically shown in FIG. 12B.

[0015] When the two electrodes 201 and 202 short-circuit in the defectportion 204, the defect portion 204 supposedly has a resistance R_(SC)and connects the two electrodes of the EL element 200 to one another.Then, when a current flowing in the defect portion 204 is given asI_(SC) and a current flowing in the EL layer 203 is given as I_(d10), aforward current I_(on) caused to flow from one of the electrodes of theEL element satisfies the following equation:

I _(on) =I _(SC) +Id10

[0016] Therefore, when I_(on) is constant in the above equationI_(on)=I_(SC)+I_(d10), the current I_(dio) that actually flows in the ELlayer 203 is reduced in the EL element having the defect portion. Thistendency is enhanced when the resistance R_(SC) in the defect portion204 is small and I_(SC) is accordingly large, thereby increasing theneed for rectification in the EL element 200.

[0017] When the current I_(d10) flowing in the EL layer 203 is small,the luminance of light emitted from the EL element 200 is also small. Inother words, the short circuit in the defect portion causes the ELelement to emit light of lower luminance upon application of a forwardbias voltage than in the case where no short circuit takes place.

[0018] The results are the same even when the EL layer is a laminate ofplural layers and the pin hole formed in the light emitting layerconnects a hole injection layer or a hole transporting layer to anelectron injection layer or an electron transporting layer. The portionwhere the hole injection layer or the hole transporting layer isconnected to the electron injection layer or the electron transportinglayer receives a reverse bias current flow similar to the defect portionwhere the electrodes short-circuit. Therefore, this portion can also bea cause of the EL element emitting light of low luminance. Hereinafter,every portion where two layers sandwiching a light emitting layer areconnected to each other in a pin hole formed in the light emitting layeris generically called a defect portion.

[0019] In addition to lowering the luminance of light emitted from theEL element, the short circuit in the defect portion acceleratesdegradation of a part of the EL layer that surrounds the defect portionsince there is always a current flow in the defect portion.

SUMMARY OF THE INVENTION

[0020] The present invention has been made in view of the aboveproblems, and an object of the present invention is to present a methodof repairing a defect portion.

[0021] The present inventors have thought that, even though an ELelement has a defect portion, reduction of current flowing in an ELlayer when a forward bias voltage is applied can be avoided byincreasing the resistance in the defect portion.

[0022] Thus devised is a method of increasing a resistance R_(SC) in thedefect portion by applying a reverse bias voltage to the EL element tocause a reverse bias current I_(rev) to flow.

[0023] When the reverse bias current I_(rev) is caused to flow in the ELelement, most part of it flows into the defect portion where the shortcircuit takes place instead of flowing into the EL layer. If a largecurrent flows through the defect portion, the temperature in the defectportion is raised to cause some changes in the defect portion, includingburnout of the defect portion, vaporization of the defect portion, andtransform of the defect portion into an insulator due to oxidization orcarbonization. As a result of the changes, the resistance R_(SC) isincreased. In this specification, the defect portion whose resistanceR_(SC) is increased by a reverse bias current flowing thereinto iscalled a transmuted portion.

[0024] With the resistance R_(SC) increased, the current flowing intothe transmuted portion when a forward bias voltage is applied to the ELelement is reduced whereas the current flowing into the EL layer isincreased, thereby raising the luminance of emitted light.

[0025] Having high resistance R_(SC), the transmuted portion hardlyallows a current to flow therein in contrast to the defect portion wherethere is always a flow of current to accelerate degradation of a part ofthe EL layer that surrounds the defect portion. Therefore, degradationis not accelerated in a part of the EL layer that surrounds thetransmuted portion.

[0026] The fabricating and/or repairing method of the present inventionis applicable not only to an active matrix light emitting device butalso to a passive matrix light emitting device. The structure of thepresent invention will be shown below.

[0027] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device by applying a firstvoltage and a second voltage to an EL element in order, characterized inthat the first voltage and the second voltage are reverse bias voltagesof different levels.

[0028] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device by graduallychanging a voltage applied to an EL element from a first voltage to asecond voltage, characterized in that the first voltage and the secondvoltage are reverse bias voltages of different levels.

[0029] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode, an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a first voltage and a second voltageare applied in order between the anode and the cathode, and the firstvoltage and the second voltage are reverse bias voltages of differentlevels.

[0030] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode. an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a voltage applied between the anodeand the cathode is gradually changed from a first voltage to a secondvoltage, and the first voltage and the second voltage are reverse biasvoltages of different levels.

[0031] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode. an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a first voltage and a second voltageare applied in order between the anode and the cathode, thereby making aportion where a reverse-bias current flows between the anode and thecathode insulating or highly resistive, and the first voltage and thesecond voltage are reverse bias voltages of different levels.

[0032] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode, an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a voltage applied between the anodeand the cathode is gradually changed from a first voltage to a secondvoltage, thereby making a portion where a reverse-bias current flowsbetween the anode and the cathode insulating or highly resistive, andthe first voltage and the second voltage are reverse bias voltages ofdifferent levels.

[0033] According to the present invention, a method of fabricatingand/or repairing a light emitting device can be characterized in thatthe first voltage and the second voltage are within ±15% of an avalanchevoltage of the EL element.

[0034] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device by applying a firstvoltage and a second voltage to an EL element in order, characterized inthat the first voltage is a ground voltage while the second voltage is areverse bias voltage.

[0035] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device by graduallychanging a voltage applied to an EL element from a first voltage to asecond voltage, characterized in that one of the first voltage and thesecond voltage is a ground voltage while the other is a reverse biasvoltage.

[0036] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode, an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a first voltage and a second voltageare applied in order between the anode and the cathode, and the firstvoltage is a ground voltage while the second voltage is a reverse biasvoltage.

[0037] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode, an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a voltage applied between the anodeand the cathode is gradually changed from a first voltage to a secondvoltage, and one of the first voltage and the second voltage is a groundvoltage while the other is a reverse bias voltage.

[0038] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode, is an EL layer, and a cathode, the ELlayer being in contact with the anode and the cathode being in contactwith the EL layer, characterized in that a first voltage and a secondvoltage are applied in order between the anode and the cathode, therebymaking a portion where a reverse-bias current flows between the anodeand the cathode insulating or highly resistive, and the first voltage isa ground voltage while the second voltage is a reverse bias voltage.

[0039] According to the present invention, there is provided a method offabricating and/or repairing a light emitting device having an ELelement that includes an anode, an EL layer, and a cathode, the EL layerbeing in contact with the anode and the cathode being in contact withthe EL layer, characterized in that a voltage applied between the anodeand the cathode is gradually changed from a first voltage to a secondvoltage, thereby making a portion where a reverse-bias current flowsbetween the anode and the cathode insulating or highly resistive, andone of the first voltage and the second voltage is a ground voltagewhile the other is a reverse bias voltage.

[0040] According to the present invention, a method of fabricatingand/or repairing a light emitting device can be characterized in thatthe reverse bias voltage is within ±15% of an avalanche voltage of theEL element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In the accompanying drawings:

[0042]FIGS. 1A and 1B are diagrams schematically showing the currentflow in an EL element when a reverse bias voltage is applied to the ELelement;

[0043]FIGS. 2A and 2B are diagrams schematically showing a change involtage-current characteristic of an EL element in the middle ofrepairing process and the current flow in the EL element when a forwardbias voltage is applied to the EL element after repairing;

[0044]FIG. 3 is a circuit diagram of a pixel;

[0045]FIGS. 4A and 4B are circuit diagrams of a pixel portion and adiagram showing the operation of the pixel portion during repairing,respectively;

[0046]FIG. 5 is a circuit diagram of a pixel;

[0047]FIGS. 6A and 6B are circuit diagrams of a pixel portion and adiagram showing the operation of the pixel portion during repairing,respectively.

[0048]FIGS. 7A and 7B are diagrams showing the structure of drivingcircuits;

[0049]FIGS. 8A and 8B are diagrams showing the structure of drivingcircuits;

[0050]FIGS. 9A and 9B are diagrams showing the structure of EL elements;

[0051]FIGS. 10A and 10B are diagrams showing the structure of ELelements;

[0052]FIGS. 11A to 11H are diagrams showing electric equipment havinglight emitting devices to which a repairing method of the presentinvention is applied;

[0053]FIGS. 12A and 12B are respectively a sectional view of an ELelement having a defect portion and a diagram schematically showing thecurrent flow when a forward bias current flows in the EL element;

[0054]FIGS. 13A and 13B are diagrams showing the voltage-currentcharacteristic of EL elements;

[0055]FIG. 14 is a graph showing the voltage-current characteristic ofan EL element when a reverse bias current flows therein;

[0056]FIG. 15 is a diagram showing the voltage-current characteristic ofan EL element;

[0057]FIG. 16 is a sectional view of a light emitting device:

[0058]FIG. 17 is a sectional view of a light emitting device;

[0059]FIG. 18 is a sectional view of a light emitting device; and

[0060]FIGS. 19A and 19B are diagrams of a passive matrix light emittingdevice to which a repairing method of the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] [Embodiment Mode]

[0062] A fabricating and/or repairing method of the present inventionwill be described with reference to FIGS. 1A and 1B. FIG. 1A is adiagram schematically showing the current flow in an EL element having adefect portion when a reverse bias voltage is applied to the EL element.

[0063] A ground voltage GND and a reverse bias voltage V_(rev) arealternately applied to the EL element. FIG. 1B is a timing chart of whenthe ground voltage GND and the reverse bias voltage V_(rev) arealternately applied. Note that the present invention is not limited tothe structure of this embodiment mode, namely, alternate application ofthe ground voltage GND and the reverse bias voltage V_(rev). Theinvention only requires application of a reverse bias voltage to the ELelement. Accordingly, the combination of voltages to be appliedalternately to the EL element may be a combination of a forward voltageand the reverse bias voltage V_(rev), or a combination of the reversebias voltage V_(rev) and a reverse bias voltage that is not equal withV_(rev).

[0064] In this embodiment mode, the reverse bias voltage is applied tothe EL element at given time intervals. However, the present inventionis not limited thereto and a direct reverse bias voltage may be appliedto the EL element.

[0065] The reverse bias voltage is gradually increased until avalanchetakes place to cause an avalanche current to flow into the EL element inthis embodiment mode. The voltage at which the avalanche current startsto flow into the EL element is herein called an avalanche voltage.However, the present invention is not limited thereto and the level ofvoltage to be applied to the EL element can be set suitably by adesigner. An appropriate level of voltage applied to the EL element ishigh enough to transmute the defect portion but is not so high as todamage the El element or degrade its EL layer.

[0066] The voltage level is gradually increased also when the voltage isa direct reverse bias voltage.

[0067] Alternatively, a reverse bias voltage of constant level may beapplied to the EL element at given time intervals or a direct reversebias voltage of constant level may be applied.

[0068] By applying a reverse bias voltage to the EL element at giventime intervals, it is possible to prevent a part of the EL layer thatsurrounds the defect portion from being degraded by heat generated fromapplication of the reverse bias voltage.

[0069] The gradual increase in level of the reverse bias voltage makesit easy to find the level of reverse bias voltage that is optimal forrepairing that particular EL element.

[0070] When the reverse bias voltage V_(rev) is applied to the ELelement, a reverse bias current I_(rev) flows into the EL element. Thereverse bias current I_(rev) satisfies I_(rev)=I_(d10)+I_(SC), whereinI_(d10) represents a current flowing in an EL layer 103 and I_(SC)represents a current flowing in a defect portion 104. However, thereverse bias current hardly flows into the EL layer and I_(rev)≈I_(SC)is assumed.

[0071] When the current I_(rev) flows into the defect portion 104, thetemperature in the defect portion 104 is raised to cause burnout of thedefect portion, vaporization of the defect portion, or transform of thedefect portion into an insulator due to oxidization or carbonization,thereby changing the defect portion into the transmuted portion. Aresistance R_(SC) is thus increased.

[0072]FIG. 2A shows a change with time in voltage-current characteristicof the EL element having the defect portion 104 when the repairingmethod of the present invention is employed. The voltage-currentcharacteristic curve shifts with time toward directions indicated byarrows. V_(av) represents the avalanche voltage. Upon application of areverse bias voltage, the resistance R_(SC) of the defect portionincreases as the time elapses accompanied by reduction of the currentI_(SC) that flows through the defect portion. The amount of currentflowing into the EL element is thus reduced.

[0073]FIG. 2B schematically shows the current flow in the EL elementwhen a forward bias voltage is applied to the EL element. A reduction ofthe current I_(SC) flowing through the defect portion results in anincrease in current I_(d10) that actually flows into the EL layer when aforward bias voltage is applied to the EL element. thereby raising theluminance of emitted light.

[0074] The method of the present invention can increase the amount ofcurrent actually flowing through the EL layer upon application of aforward bias voltage to the EL element even if a pin hole is formed inthe EL layer during formation of the layer due to dusts or the like andtwo layers sandwiching a light emitting layer short-circuit, because themethod can raise the resistance of the defect portion where the shortcircuit takes place by changing the defect portion into the transmutedportion. Therefore the repairing method of the present invention canraise the luminance of emitted light with application of the same levelof voltage despite the presence of the defect portion.

[0075] Having high resistance R_(SC), the transmuted portion hardlyallows a current to flow therein in contrast to the defect portion wherethere is always a flow of current to accelerate degradation of a part ofthe EL layer that surrounds the defect portion. Therefore, degradationis not accelerated in a part of the EL layer that surrounds thetransmuted portion.

[0076] Embodiments of the present invention will be described below.

[0077] [Embodiment 1]

[0078] This embodiment gives a description on a case of applying arepairing method of the present invention to an active matrix lightemitting device that has two thin film transistors (TFTs) in each pixel.

[0079]FIG. 3 is a circuit diagram of a pixel in the light emittingdevice to which the repairing method of the present invention isapplied. Each pixel has a source signal line Si (i represents one ofintegers from 1 to x), a power supply line Vi (i represents one ofintegers from 1 to x), and a gate signal line Gj (j represents one ofintegers from 1 to y).

[0080] Each pixel also has a switching TFT 301, an EL driving TFT 302,an EL element 303, and a capacitor 304.

[0081] The switching TFT 301 has a gate electrode connected to the gatesignal line Gj. The switching TFT 301 has a source region and a drainregion one of which is connected to the source signal line Si and theother of which is connected to a gate electrode of the EL driving TFT302.

[0082] The EL driving TFT 302 has a source region connected to the powersupply line Vi, and has a drain region connected to one of twoelectrodes of the EL element 303. The other electrode of the twoelectrodes of the EL element 303, namely, the electrode that is notconnected to the drain region of the EL driving TFT 302, is connected toan opposite power supply 307.

[0083] Of the two electrodes of the EL element 303, the one that isconnected to the drain region of the EL driving TFT 302 is called apixel electrode while the other that is connected to the opposite powersupply 307 is called an opposite electrode.

[0084] The capacitor 304 is formed between the gate electrode of the ELdriving TFT is 302 and the power supply line Vi.

[0085]FIG. 4A shows a pixel portion of the light emitting device whichhas a plurality of pixels shown in FIG. 3. A pixel portion 306 hassource signal lines S1 to Sx, power supply lines V1 to Vx, and gatesignal lines G1 to Gy. The plural pixels 305 form a matrix in the pixelportion 306.

[0086]FIG. 4B shows the operation of the TFTs and the level of voltageto be inputted to the power supply line Vi and to the opposite electrodein each pixel during repairing a defect portion of the EL element 303.When the defect portion of the EL element 303 is to be repaired, theswitching TFT 301 and the EL driving TFT 302 in each pixel are bothturned ON. While the voltage of the power supply line Vi is keptconstant. the voltage of the opposite electrode is changed at given timeintervals so that a given reverse bias current flows into the EL elementat given time intervals.

[0087] The defect portion of the EL element may be repaired at once inall of the pixels 305 of the pixel portion 306. Alternatively, therepair may be performed on one line of pixels at a time, or on one pixelat a time.

[0088] The method of the present invention can increase the amount ofcurrent actually flowing through the EL layer upon application of aforward bias voltage to the EL element even if a pin hole is formed inthe EL layer during formation of the layer due to dusts or the like andtwo layers sandwiching a light emitting layer short-circuit, because themethod can raise the resistance of the defect portion where the shortcircuit takes place by changing the defect portion into the transmutedportion. Therefore the repairing method of the present invention canraise the luminance of emitted light with application of the same levelof voltage despite the presence of the defect portion.

[0089] Having high resistance R_(SC), the transmuted portion hardlyallows a current to flow therein in contrast to the defect portion wherethere is always a flow of current to accelerate degradation of a part ofthe EL layer that surrounds the defect portion. Therefore, degradationis not accelerated in a part of the EL layer that surrounds thetransmuted portion.

[0090] Note that application of the repairing method of the presentinvention is not limited to light emitting devices structured as above.The present invention can be applied to light emitting devices of anystructure.

[0091] [Embodiment 2]

[0092] This embodiment gives a description on a case of applying arepairing method of the present invention to an active matrix lightemitting device that has three thin film transistors (TFTs) in eachpixel.

[0093]FIG. 5 is a circuit diagram of a pixel in the light emittingdevice to which the repairing method of the present invention isapplied. Each pixel has a source signal line Si (i represents one ofintegers from 1 to x), a power supply line Vi (i represents one ofintegers from 1 to x), a writing gate signal line Gaj (j represents oneof integers from 1 to y) and an erasing gate signal line Gej (jrepresents one of integers from 1 to y).

[0094] Each pixel also has a switching TFT 501 a, an erasing TFT 501 b,an EL driving TFT 502, an EL element 503, and a capacitor 504.

[0095] The switching TFT 501 a has a gate electrode connected to thewriting gate signal line Gaj. The switching TFT 501 a has a sourceregion and a drain region one of which is connected to the source signalline Si and the other of which is connected to a gate electrode of theEL driving TFT 502.

[0096] The erasing TFT 501 b has a gate electrode connected to theerasing gate signal line Gej. The erasing TFT 501 has a source regionand a drain region one of which is connected to the power supply line Viand the other of which is connected to the gate electrode of the ELdriving TFT 502.

[0097] The EL driving TFT 502 has a source region connected to the powersupply line Vi, and has a drain region connected to one of twoelectrodes of the EL element 503. The other electrode of the twoelectrodes of the EL element 503, namely, the electrode that is notconnected to the drain region of the EL driving TFT 502, is connected toan opposite power supply 507.

[0098] Of the two electrodes of the EL element 503, the one that isconnected to the drain region of the EL driving TFT 502 is called apixel electrode while the one that is connected to the opposite powersupply 507 is called an opposite electrode.

[0099] The capacitor 504 is formed between the gate electrode of the ELdriving TFT 502 and the power supply line Vi.

[0100]FIG. 6A shows a pixel portion of the light emitting device whichhas a plurality of pixels shown in FIG. 5. A pixel portion 506 hassource signal lines S1 to Sx, power supply lines V1 to Vx, writing gatesignal lines Ga1 to Gay, and erasing gate signal lines Ge1 to Gey. Theplural pixels 505 form a matrix in the pixel portion 506.

[0101]FIG. 6B shows the operation of the TFTs and the level of voltageto be inputted to the power supply line Vi and to the opposite electrodein each pixel during repairing a defect portion of the EL element 503.When the defect portion of the EL element 503 is to be repaired, theswitching TFT 501 a and the EL driving TFT 502 in each pixel are bothturned ON. The erasing TFT 501 b in each pixel is turned OFF. While thevoltage of the power supply line Vi is kept constant, the voltage of theopposite electrode is changed at given time intervals so that a givenreverse bias current flows into the EL element 503 at given timeintervals.

[0102] The defect portion of the EL element 503 may be repaired at oncein all of the pixels 505 of the pixel portion 506. Alternatively, therepair may be performed on one line of pixels at a time, or on one pixelat a time.

[0103] The method of the present invention can increase the amount ofcurrent actually flowing through the EL layer upon application of aforward bias voltage to the EL element even if a pin hole is formed inthe EL layer during formation of the layer due to dusts or the like andtwo layers sandwiching a light emitting layer short-circuit, because themethod can raise the resistance of the defect portion where the shortcircuit takes place by changing the defect portion into the transmutedportion. Therefore the repairing method of the present invention canraise the luminance of emitted light with application of the same levelof voltage despite the presence of the defect portion.

[0104] Having high resistance R_(SC), the transmuted portion hardlyallows a current to flow therein in contrast to the defect portion wherethere is always a flow of current to accelerate degradation of a part ofthe EL layer that surrounds the defect portion. Therefore, degradationis not accelerated in a part of the EL layer that surrounds thetransmuted portion.

[0105] [Embodiment 3]

[0106] In this embodiment, the structure of the driver circuit which isdriving the pixel portion in Embodiment 1 is explained in Embodiment 1.The source signal driving circuit and the gate signal driving circuitwhich are driving the pixel portion in Embodiment 1 are not limited tothe structure shown in this Embodiment.

[0107]FIG. 7 shows a driving circuit of the light emitting device by ablock figure. In FIG. 7A, the reference numeral 601 is a source signalline driver circuit which has the shift register 602, the latch (A) 603and the latch (B) 604.

[0108] A clock signal (CLK) and a start pulse (SP) are inputted to theshift register 602 in the source signal line driving circuit 601. Theshift register 602 generates timing signals in order based upon theclock signal (CLK) and the start pulse (SP), and the timing signals aresupplied one after another to downstream circuits through a buffer (notshown in the figure).

[0109] Note that the timing signals from the shift register 602 may bebuffer-amplified by a circuit such as a buffer. The load capacitance(parasitic capacitance) of a wiring to which the timing signals aresupplied is large because many of the circuits and elements areconnected to the wiring. The buffer is formed in order to preventdullness in the rise and fall of the timing signal, generated due to thelarge load capacitance. In addition, the buffer is not always necessaryformed.

[0110] The timing signals which is a buffer-amplified are supplied tothe latch (A) 603. The latch (A) 603 has a plurality of latch stages forprocessing an n-bit digital signal (digital signal having an imageinformation). The latch (A) 603 writes in and maintains an n-bit digitalsignal which is supplied by the external of the source signal linedriver circuit 601 in order simultaneously with the input of theabove-mentioned timing signals.

[0111] Note that the digital signals may be sequentially inputted to theplurality of latch stages of the latch (A) 603 when the digital signalsare taken in by the latch (A) 603. However, the present invention is notlimited to this structure. A so-called division drive may be performed,that is, the plurality of latch stages of the latch (A) 603 is dividedinto a number of groups, and then the digital signals are parallelinputted to the respective groups at the same time. Note that the numberof groups at this point is called a division number. For example, if thelatch circuits are grouped into 4 stages each, then it is called a4-branch division drive.

[0112] The time necessary to complete writing of the digital signalsinto all the latch stages of the latch (A) 603 is called a line period.In effect, the above-defined line period added with the horizontalretrace period may also be referred to as the line period.

[0113] After the completion of one line period, a latch signal issupplied to the latch (B) 604. In this moment, the digital signalswritten in and held by the latch (A) 603 are sent all at once to thelatch (B) 604 to be written in and held by all the latch stages thereof.

[0114] Sequential writing-in of digital signals on the basis of thetiming signals from the shift register 602 is again carried out to thelatch (A) 603 after it has completed sending the digital signals to thelatch (B) 604.

[0115] During this second time one line period, the digital videosignals written in and held by the latch (B) 603 are inputted to thesource signal lines.

[0116]FIG. 7B is a block figure which is showing a structure of the gatesignal line driver circuit.

[0117] The gate signal driver circuit 605 has a shift resister 606 and abuffer 607 respectively. According to circumstances, the level shiftercan be provided.

[0118] In the gate signal line driving circuit 605, the timing signal issupplied to the buffer 607 from the shift register 606, and this issupplied to a corresponding gate signal line. Gate electrodes of theswitching TFTs of one line portion of pixels are connected to each ofthe gate signal lines. All of the switching TFTs of the one line portionof pixels must be placed in an ON state simultaneously, and therefore abuffer in which a large electric current can flow is used.

[0119] In the case that the repair method of the present invention isused, the switching TFT is in an ON state by controlling a signalinputted to the gate signal line by the gate signal line driver circuit,and the EL driver TFT is in an ON state by a digital signal inputted tothe source signal line from the source signal line driver circuit.

[0120] Further, in this embodiment, the structure of the driver circuitof the pixel portion shown in Embodiment 1 is explained, but also thestructure of the driver circuit of the is pixel portion shown inEmbodiment 2 has the same structure. The pixel portion shown inEmbodiment 2 has a two gate signal line driver circuit, and each gatesignal line driver circuit has structures shown in FIG. 7B respectively.In Embodiment 2, each gate signal line driver circuit control theinputting signal to the writing gate signal line and the eraser gatesignal line respectively.

[0121] [Embodiment 4]

[0122] A description given in this embodiment is of a structure of adriving circuit for driving the pixel portion of the light emittingdevice shown in Embodiment 1. The structure of this embodiment isdifferent from the one described in Embodiment 3. A source signal linedriving circuit and a gate signal line driving circuit for driving thepixel portion of Embodiment 1 may not necessarily have the structureshown in this embodiment.

[0123]FIG. 8A is a circuit diagram of a source signal line drivingcircuit 611 according to this embodiment. Reference numeral 612 denotesa shift register; 613, a level shifter; and 614, a sampling circuit.

[0124] A clock signal (CLK) and a start pulse signal (SP) are inputtedto the shift register 612. An analog signal containing image information(analog video signal) is inputted to the sampling circuit 614.

[0125] Upon input of the clock signal (CLK) and the start pulse signal(SP) in the shift register 612, a timing signal is generated andinputted to the level shifter 613. The timing signal inputted to thelevel shifter 613 is inputted to the sampling circuit 614 with itsamplitude amplified.

[0126] Using the timing signal inputted to the sampling circuit 614, theanalog video signal also inputted to the sampling circuit 614 is sampledand then inputted to the associated source signal line.

[0127]FIG. 8B is a block diagram showing the structure of a gate signalline driving circuit.

[0128] A gate signal line driving circuit 615 has a shift register 616and a buffer 617. The circuit may also have a level shifter.

[0129] In the gate signal line driving circuit 615, a timing signal issupplied from the shift register 616 to the buffer 617, and then to theassociated gate signal line. The gate signal line is connected to gateelectrodes of switching TFTs in one line of pixels. Since switching TFTsin one line of pixels have to be turned ON at once, the buffer used hasto be capable of flowing a large current.

[0130] When the repairing method of the present invention is used, thegate signal line driving circuit controls signals to be inputted to gatesignal lines to turn switching TFTs ON whereas EL driving TFTs areturned ON by analog video signals inputted to source signal lines fromthe source signal line driving circuit.

[0131] [Embodiment 5]

[0132] This embodiment describes a case of applying a repairing methodof the present invention to an EL element whose EL layer comprises aplurality of layers.

[0133]FIG. 9A shows the structure of the EL element. First, a holeinjection layer is formed by spin coating to a thickness of 30 nm fromPEDOT that is a polythiophene derivative on an anode formed of acompound of indium oxide and tin oxide (ITO). Next, an MTDATA layer witha thickness of 20 nm and an α-NPD layer with a thickness of 10 nm areformed by evaporation as a hole transporting layer. On the holetransporting layer, a light emitting layer is formed of a self-luminousmaterial, Alq₃, that is a singlet compound by evaporation to a thicknessof 50 nm. Then a cathode is formed by depositing Yb through evaporationto a thickness of 400 nm to complete the EL element.

[0134] If a pin hole is opened and a defect portion is formed in thelight emitting layer of the EL element structured as above, the Yb layerthat is the cathode is undesirably brought into contact with the α-NPDlayer that is the hole transporting layer in the defect portion.

[0135] When a reverse bias current is caused to flow in the EL elementhaving the defect portion at given time intervals, the temperature inthe defect portion is raised so that the defect portion is burnt out,vaporized, or oxidized or carbonized to be transformed into aninsulator. As a result, the defect portion is changed into thetransmuted portion to increase the resistance thereof. Thereforedegradation of a part of the EL layer that surrounds the transmutedportion is not accelerated.

[0136] Light emitted from this EL element utilizes singlet excitationenergy from the singlet compound.

[0137]FIG. 9B shows the structure of another EL element. First, a holeinjection layer is formed by evaporation to a thickness of 20 nm fromcopper phthalocyanine on an anode formed of a compound of indium oxideand tin oxide. Next, a hole transporting layer is formed from α-NPD byevaporation to a thickness of 10 nm. On the hole transporting layer, alight emitting layer is formed of self-luminous materials, Ir(ppy)₃ andCBP, that are triplet compounds by evaporation to a thickness of 20 nm.An electron transporting layer is formed on the light emitting layer byforming a BCP layer with a thickness of 10 nm and an Alq₃ layer with athickness of 40 nm through evaporation. Then a cathode is formed bydepositing Yb through evaporation to a thickness of 400 nm to completethe EL element.

[0138] If a pin hole is opened and a defect portion is formed in thelight emitting layer of the EL element structured as above, the BCPlayer that is the electron transporting layer is undesirably broughtinto contact with the α-NPD layer that is the hole transporting layer inthe defect portion.

[0139] When a reverse bias current is caused to flow in the EL elementhaving the defect portion at given time intervals, the temperature inthe defect portion is raised so that the defect portion is burnt out,vaporized, or oxidized or carbonized to be transformed into aninsulator. As a result, the defect portion is changed into thetransmuted portion to increase the resistance thereof. Thereforedegradation of a part of the EL layer that surrounds the transmutedportion is not accelerated.

[0140] Light emitted from this EL element utilizes triplet excitationenergy from the triplet compounds.

[0141]FIG. 10A shows the structure of still another EL element. First, ahole injection layer is formed by spin coating to a thickness of 30 nmfrom PEDOT that is a polythiophene derivative on an anode formed of acompound of indium oxide and tin oxide (ITO). On the hole injectionlayer, a light emitting layer is formed of a self-luminous material,Alq₃, that is a singlet compound by evaporation to a thickness of 50 nm.Then a cathode is formed by depositing Pb through evaporation to athickness of 400 nm to complete the EL element.

[0142] If a pin hole is opened and a defect portion is formed in thelight emitting layer of the EL element structured as above, the Pb layerthat is the cathode is undesirably brought into contact with the PEDOTlayer that is the hole injection layer in the defect portion.

[0143] When a reverse bias current is caused to flow in the EL elementhaving the defect portion at given time intervals, the temperature inthe defect portion is raised so that the defect portion is burnt out,vaporized, or oxidized or carbonized to be transformed into aninsulator. As a result, the defect portion is changed into thetransmuted portion to increase the resistance thereof. Thereforedegradation of a part of the EL layer that surrounds the transmutedportion is not accelerated.

[0144] Light emitted from this EL element utilizes singlet excitationenergy from the singlet compound.

[0145]FIG. 10B shows the structure of yet still another EL element.First, a cathode is formed by evaporation from Pb to a thickness of 400nm. On the cathode, a light emitting layer is formed of a self-luminousmaterial, Alq₃, that is a singlet compound by evaporation to a thicknessof 50 nm. Next, a hole injection layer is formed by spin coating to athickness of 30 nm from PEDOT that is a polythiophene derivative. An Aufilm with a thickness of 5 nm is formed thereon. The Au film is providedto prevent degradation of a surface of the EL layer in later steps. Thenan anode is formed on the Au film from a compound of indium oxide andtin oxide (ITO) to complete the EL element.

[0146] If a pin hole is opened and a defect portion is formed in thelight emitting layer of the EL element structured as above, the Pb layerthat is the cathode is undesirably brought into contact with the PEDOTlayer that is the hole injection layer in the defect portion.

[0147] When a reverse bias current is caused to flow in the EL elementhaving the defect portion at given time intervals, the temperature inthe defect portion is raised so that the defect portion is burnt out,vaporized, or oxidized or carbonized to be transformed into aninsulator. As a result, the defect portion is changed into thetransmuted portion to increase the resistance thereof Thereforedegradation of a part of the EL layer that surrounds the transmutedportion is not accelerated.

[0148] Light emitted from this EL element utilizes singlet excitationenergy from the singlet compound.

[0149] With the above structure, the present invention can increase theamount of current actually flowing through the EL layer upon applicationof a forward bias voltage to the EL element even if a pin hole is formedin the EL layer during formation of the layer due to dusts or the likeand two layers sandwiching a light emitting layer short-circuit, becausethe method can raise the resistance of the defect portion where theshort circuit takes place by changing the defect portion into thetransmuted portion. Therefore the repairing method of the presentinvention can raise the luminance of emitted light with application ofthe same level of voltage despite the presence of the defect portion.

[0150] Furthermore, the invention can prevent accelerated degradation ina part of the EL layer that surrounds the defect portion by changing thedefect portion into the transmuted portion to increase the resistancethereof.

[0151] A carbide generated by carbonization of an EL material is high ininsulating property and is stable as a substance. For that reason, therepairing method of the present invention is particularly effective whenthe defect portion is filled with an organic EL material, for example,when the defect portion is formed in an EL layer that is in contact withan EL material film.

[0152] This embodiment may be combined freely with Embodiments 1 through4.

[0153] [Embodiment 6]

[0154] In this embodiment, an external light emitting quantum efficiencycan be remarkably improved by using an EL material by whichphosphorescence from a triplet exciton can be employed for emitting alight. As a result, the power consumption of the EL element can bereduced, the lifetime of the EL element can be elongated and the weightof the EL element can be lightened.

[0155] The following is a report where the external light emittingquantum efficiency is improved by using the triplet exciton (T. Tsutsui,C. Adachi, S. Saito, Photochemical Processes in Organized MolecularSystems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo, 1991) p. 437).

[0156] The molecular formula of an EL material (coumarin pigment)reported by the above article is represented as follows.

[0157] (M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M.E. Thompson, S. R. Forrest, Nature 395 (1998) p.151)

[0158] The molecular formula of an EL material (Pt complex) reported bythe above article is represented as follows.

[0159] (M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R.Forrest, Appl. Phys. Lett., 75 (1999) p.4.) (T. Tsutsui, M.-J. Yang, M.Yahiro, K. Nakamura. T. Watanabe, T. Tsuji, Y. Fukuda, T. Wakimoto, S.Mayaguchi, Jpn, Appl. Phys., 38 (12B) (1999) L1502)

[0160] The molecular formula of an EL material (Ir complex) reported bythe above article is represented as follows.

[0161] As described above, if phosphorescence from a triplet exciton canbe put to practical use, it can realize the external light emittingquantum efficiency three to four times as high as that in the case ofusing fluorescence from a singlet exciton in principle.

[0162] The structure according to this embodiment can be freelyimplemented in combination of any structures of the Embodiments 1 to 5.

[0163] [Embodiment 7]

[0164] This embodiment describes the actual voltage-currentcharacteristic of an EL element having a defect portion when a reversebias voltage is applied to the EL element.

[0165] The EL element used in this embodiment is structured as follows.First, a hole injection layer is formed by evaporation to a thickness of20 nm from copper phthalocyanine on an anode formed of a compound ofindium oxide and tin oxide (ITO). Next, an MTDATA layer with a thicknessof 20 nm and an α-NPD layer with a thickness of 10 nm are formed byevaporation as a hole transporting layer. On the hole transportinglayer, a light emitting layer is formed of a self-luminous material,Alq₃, that is a singlet compound by evaporation to a thickness of 50 nm.An electron injection layer is formed next from lithium acetylacetonate(Liacac) to a thickness of 2 nm. Then a cathode is formed from analuminum alloy to a thickness of 50 nm to complete the EL element.

[0166]FIG. 14 shows the voltage-current characteristic of the EL elementstructured as above when a reverse bias voltage is applied to the ELelement. The reverse bias current becomes larger toward Point A at whichthe reverse bias voltage is −5 V and declines past that point.

[0167] Despite the EL element being damaged, the reverse bias currentincreases, owing supposedly to application of reverse bias voltage, butdeclines past Point A. Therefore it can be deduced that some change indefect portion takes place at Point A to raise the resistance of thedefect portion.

[0168] In the repairing method of the present invention, the level ofreverse bias voltage to be applied to the EL element and voltageapplication time varies depending on the material of an anode, acathode, and an EL layer of the EL element and the structure of the ELelement. If the reverse bias voltage is remarkably low, effects of thepresent invention cannot be obtained but in as case of being remarkablyhigh a reverse bias voltage accelerates degradation of the EL layer ordamages the EL element itself.

[0169] According to the voltage-current characteristic shown in FIG. 14,the reverse bias current sharply increases with a reverse bias voltageof −6.5 V or lower. Therefore, in the case of the EL element used inthis embodiment, the EL element is probably about to be damaged or theEL layer comes near to degrade when a reverse bias voltage of −6.5 orlower is applied.

[0170] The level of reverse bias voltage to be applied to the EL elementand voltage application time have to be set by one who intends to carryout the present invention so as to suit the material of an anode, acathode, and an EL layer of the EL element and the structure of the ELelement.

[0171] [Embodiment 8]

[0172] This embodiment describes the voltage-current characteristic ofan EL element in the case where a direct reverse bias voltage isincreased until it reaches an avalanche voltage (V_(av)) and thendecreased.

[0173]FIG. 15 is a graph of the voltage-current characteristic when adirect reverse bias voltage is increased until the avalanche voltage(V_(av)) and then decreased. As the reverse bias voltage is increased, areverse bias current I_(rev) temporarily surges at Point B. Point C, andPoint D, where some change takes place in the defect portion totransform the defect portion into the transmuted portion.

[0174] No particular change in reverse bias current I_(rev) is observedas the reverse bias voltage V_(rev) declines after the voltage reachesthe highest at V_(av).

[0175] This embodiment may be combined freely with Embodiments 1 through7.

[0176] [Embodiment 9]

[0177] This embodiment gives descriptions on a sectional view of a lightemitting device to which a repairing method of the present invention isapplied.

[0178] In FIG. 16, an n-channel TFT is used for a switching TFT 721formed on a substrate 700.

[0179] The switching TFT 721 in this embodiment has a double gatestructure in which two channel formation regions are formed. However,the TFT may take a single gate structure having one channel formationregion or a triple gate structure having three channel formationregions.

[0180] A driving circuit formed on the substrate 700 has an n-channelTFT 723 and a p-channel TFT 724. Although the TFTs of the drivingcircuit are of single gate structure in this embodiment, the TFTs maytake the double gate structure or the triple gate structure.

[0181] Wiring lines 701 and 703 function as source wiring lines of theCMOS circuit whereas 702 functions as a drain wiring line thereof. Awiring line 704 functions as a wiring line that electrically connects asource wiring line 708 to a source region of the switching TFT. A wiringline 705 functions as a wiring line that electrically connects a drainwiring line 709 to a drain region of the switching TFT.

[0182] A p-channel TFT is used for an EL driving TFT 722. The EL drivingTFT 722 in this embodiment is of single gate structure but it may havethe double gate structure or the triple gate structure.

[0183] A wiring line 706 is a source wiring line of the EL driving TFT(corresponds to a current supply line). A wiring line 707 is anelectrode that is laid on a pixel electrode 710 of the EL driving TFT tobe electrically connected to the pixel electrode 710.

[0184] The pixel electrode 710 is formed of a transparent conductivefilm and serves as an anode of an EL element. The transparent conductivefilm is obtained from a compound of indium oxide and tin oxide or acompound of indium oxide and zinc oxide, or from zinc oxide, tin oxide,or indium oxide alone. The transparent conductive film may be doped withgallium. The pixel electrode 710 is formed on a flat interlayerinsulating film 711 before forming the above wiring lines. In thisembodiment, the film 711 is a planarization film made of resin and it isvery important to level the level differences caused by the TFTs withthe planarization film 711. An EL layer to be formed later is so thinthat the existence of level differences can cause light emission defect.Accordingly the surface has to be leveled before forming the pixelelectrode so that the EL layer is formed on as flat a surface aspossible.

[0185] After the wiring lines 701 to 707 are formed, a bank 712 isformed as shown in FIG. 16. The bank 712 is formed by patterning aninsulating film containing silicon, or an organic resin film, which hasa thickness of 100 to 400 nm.

[0186] Since the bank 712 is an insulating film, care must be taken notto cause static breakdown of the element during film formation. In thisembodiment, carbon particles or metal particles are added to theinsulating film that is to serve as the material of the bank 712,thereby reducing the resistivity and thus avoiding generation ofelectrostatic. The amount of carbon particles or metal particles to beadded is adjusted such that the resistivity is reduced to 1×10⁶ to1×10¹² Ωm (preferably 1×10⁸ to 1×10¹⁰ Ωm).

[0187] An EL layer 713 is formed on the pixel electrode 710. Althoughonly one pixel is shown in FIG. 16, formed in this embodiment are ELlayers for red light (R), EL layers for green light (G), and EL layersfor blue light (B). This embodiment uses for the EL layer 713 a lowmolecular weight organic EL material, which is formed into a film byevaporation. Specifically, the EL layer 713 has a laminate structure inwhich a copper phthalocyanine (CuPc) film with a thickness of 20 nm isformed as a hole injection layer 713 a and a tris-8-quinolinolatealuminum complex (Alq₃) film with a thickness of 70 nm is formed as alight emitting layer 713 b on the hole injection layer. The color ofemitted light can be controlled by choosing which fluorescent pigment,such as quinacridon, perylene, or DCM1, is used to dope Alq₃.

[0188] The material given in the above is merely an example of organicEL materials that can be used for the EL layer and there is no need tobe limited thereto. The EL layer (meaning a layer for light emission andfor carrier transportation to emit light) may have a charge carriertransporting layer or a charge carrier injection layer, or both, inaddition to the light emitting layer. For instance, a high molecularweight organic EL material may be employed for the EL layer though usedin the example shown in this embodiment is a low molecular weightorganic EL material. Inorganic materials such as silicon carbide may beused for the charge carrier transporting layer and the charge carrierinjection layer. Known organic EL materials and known inorganicmaterials can be used.

[0189] On the EL layer 713, a cathode 714 is formed from a conductivefilm. In this embodiment, an alloy film of aluminum and lithium is usedas the conductive film. A known MgAg film (an alloy film of magnesiumand silver) may of course be used. An appropriate cathode material is aconductive film made of an element belonging to Group 1 or 2 in theperiodic table, or a conductive film doped with a Group 1 or 2 element.

[0190] Formation of the cathode 714 completes an EL element 719. The ELelement 719 here means a capacitor comprising the pixel electrode(anode) 710, the EL layer 713, and the cathode 714.

[0191] It is effective to provide a passivation film 716 so as to coverthe EL element 719 completely. The passivation film 716 is an insulatingfilm, examples of which include a carbon film, a silicon nitride film,and a silicon oxynitride film. A single layer or a laminate of theseinsulating films is used for the passivation film.

[0192] It is preferable to use as the passivation film a film that cancover a wide area. A carbon film, a DLC (diamond-like carbon) film, inparticular, is effective. The DLC film can be formed in a temperaturerange between room temperature and 100° C., and therefore is easy toform above the EL layer 713 that has a low heat resistance. Furthermore,the DLC film is highly effective in blocking oxygen and can preventoxidization of the EL layer 713. Therefore the EL layer 713 can be savedfrom being oxidized before a sealing step to be carried outsubsequently.

[0193] A seal 717 is provided on the passivation film 716 and a covermember 718 is bonded. A UV-curable resin can be used as the seal 717. Itis effective to place a substance having a hygroscopic effect or asubstance having an antioxidizing effect inside the seal 717. The covermember 718 used in this embodiment is a glass substrate, a quartzsubstrate, or a plastic substrate (including a plastic film) with carbonfilms (preferably diamond-like carbon films) formed on its front andback.

[0194] Thus completed is an EL display device structured as shown inFIG. 16. It is effective to use a multi-chamber type (or in-line type)film forming apparatus to successively process the steps subsequent toformation of the bank 712 up through formation of the passivation film716 without exposing the device to the air. The successive processingfor avoiding exposure to the air may further be extended to include thestep of bonding the cover member 718.

[0195] The TFTs in this embodiment are each characterized in that: agate electrode is formed from a conductive film having two layers;almost no difference in concentration is found between low concentrationimpurity regions that are formed between a channel formation region anda drain region, thereby forming a gentle concentration gradient; and thelow concentration impurity regions are classified into one that overlapswith the underlying gate electrode (this one is called a GOLD region)and one that does not overlap the gate electrode (this one is called anLDD region). The edges of a gate insulating film, namely, a region abovethe region that does not overlap the gate electrode and above a highconcentration impurity region are tapered.

[0196] In the light emitting device of this embodiment, if there is apin hole in the light emitting layer 713 b, it causes a defect portionwhere the hole injection layer 713 a and the cathode 714 are broughtinto contact through the pin hole. The defect portion can be changedinto a transmuted portion 715 by the repairing method of the presentinvention, resulting in a raise in resistance. Therefore the other partof the pixel than the pin hole can have increased luminance anddegradation of apart of the EL layer that surrounds the pin hole is notaccelerated.

[0197] This embodiment shows the structure of the pixel portion and ofthe driving circuit only. However, the manufacturing process accordingto this embodiment can also form logic circuits such as a signal dividercircuit, a D/A converter, an operation amplifier, and a γ correctioncircuit on the same insulator which holds the pixel portion and thedriving circuit. Additionally a memory and a microprocessor may beformed.

[0198] The structure of this embodiment can be combined with any ofEmbodiments 1, 2, 3, 4, 6, and 8.

[0199] [Embodiment 10]

[0200] This embodiment gives descriptions on a sectional view of a lightemitting device to which a repairing method of the present invention isapplied.

[0201] In FIG. 17, a p-channel TFT 200 and an n-channel TFT 201 of adriving circuit are formed on the same substrate on which an EL drivingTFT 203, a switching TFT 204, and a capacitor storage 205 are formed toconstitute a pixel portion.

[0202] The p-channel TFT 200 of the driving circuit is comprised of: aconductive layer 220 having a second taper shape and functioning as agate electrode; a channel formation region 206; a third impurity region207 a to function as a source region or a drain region; a fourthimpurity region (A) 207 b serving as an LDD region that does not overlapthe gate electrode 220; and a fourth impurity region (B) 207 c servingas an LDD region that partially overlaps the gate electrode 220.

[0203] The n-channel TFT 201 of the driving circuit is comprised of: aconductive layer 221 having a second taper shape and functioning as agate electrode; a channel formation region 208; a first impurity region209 a to function as a source region or a drain region; a secondimpurity region (A) 209 b serving as an LDD region that does not overlapthe gate electrode 221; and a second impurity region (B) 209 c servingas an LDD region that partially overlaps the gate electrode 221. Whilethe channel length is 2 to 7 μm, the length of a portion where thesecond impurity region (B) 209 c overlaps the gate electrode 221 is setto 0.1 to 0.3 μm. The length of this L_(OV) region is controlled byadjusting the thickness of the gate electrode 221 and the angle of thetapered portion. With this LDD region formed in the n-channel TFT, thehigh electric field generated in the vicinity of the drain region iseased to prevent creation of hot carriers and thus prevent degradationof the TFT.

[0204] Similarly, the EL driving TFT 203 is comprised of: a conductivelayer 223 having a second taper shape and functioning as a gateelectrode; a channel formation region 212; a third impurity region 213 ato function as a source region or a drain region; a fourth impurityregion (A) 213 b serving as an LDD region that does not overlap the gateelectrode 223; and a fourth impurity region (B) 213 c serving as an LDDregion that partially overlaps the gate electrode 223.

[0205] Logic circuits such as a shift register circuit and a buffercircuit, and a sampling circuit having an analog switch constitute thedriving circuit. In FIG. 17, the TFTs of these circuits have a singlegate structure in which one gate electrode is placed between a sourceand a drain that form a pair. However, the TFTs may have a multi-gatestructure in which a plurality of electrodes are placed between thesource and the drain that form a pair.

[0206] The drain region of the EL driving TFT 203 is connected to apixel electrode 271 through a wiring line 231. An EL layer 272 is formedfrom a known organic EL material so as to contact with the pixelelectrode 271. A cathode 273 is formed so as to contact with the ELlayer 272.

[0207] The switching TFT 204 is comprised of: a conductive layer 224having a second taper shape and functioning as a gate electrode; channelformation regions 214 a and 214 b; first impurity regions 215 a and 217to function as source regions or drain regions; a second impurity region(A) 215 b serving as an LDD region that does not overlap the gateelectrode 224; and a second impurity region (B) 215 c serving as an LDDregion that partially overlaps the gate electrode 224. The length of aportion where the second impurity region (B) 215 c overlaps the gateelectrode 224 is set to 0.1 to 0.3 μm. The capacitor storage iscomprised of: a semiconductor layer extended from the first impurityregion 217 and having a second impurity region (A) 219 b, a secondimpurity region (B) 219 c, and a region 218 that is not doped with anyimpurity element for setting the conductivity type of the region; aninsulating layer of the same layer as a gate insulating film having athird shape; and a capacitor wiring line 225 that is formed form aconductive layer having a second taper shape.

[0208] In the light emitting device of this embodiment, if there is apin hole in the EL layer 272, it causes a defect portion where the pixelelectrode 271 and the cathode 273 are brought into contact through thepin hole. The defect portion can be changed into a transmuted portion274 by the repairing method of the present invention, resulting in araise in resistance. Therefore the other part of the pixel than the pinhole can have increased luminance and degradation of a part of the ELlayer that surrounds the pin hole is not accelerated.

[0209] The structure of this embodiment can be combined with any ofEmbodiments 1, 2, 3, 4, 6, and 8.

[0210] [Embodiment 11]

[0211] An outline of a cross sectional structure of a light emittingdisplay using the repair method of the present invention is explained inthis embodiment.

[0212] Reference numeral 811 denotes a substrate in FIG. 18, andreference numeral 812 denotes an insulating film which becomes a base(hereafter referred to as a base film). A light transmitting substrate,typically a glass substrate, a quartz substrate, a glass ceramicsubstrate, or a crystalline glass substrate can be used as the substrate811. However, the substrate used must be one able to withstand thehighest process temperature during the manufacturing processes.

[0213] Further, the base film 812 is particularly effective when using asubstrate containing mobile ions or a substrate which has conductivity,but the base film 812 need not be formed on a quartz substrate. Aninsulating film containing silicon may be used as the base film 812.Note that the term insulating film containing silicon specificallyindicates an insulating film such as a silicon oxide film, a siliconnitride film, and a silicon oxynitride film (denoted as SiOxNy, where xand y are arbitrary integers) containing oxygen or nitrogen atpredetermined ratios with respect to silicon.

[0214] Reference numeral 8201 denotes a switching TFT, reference numeral8202 denotes an EL driver TFT, and both are formed by n-channel TFT andp-channel TFTs respectively. When the direction of EL light emitted istoward the substrate lower side (surface where TFTs and the EL layer arenot formed), the above structure is preferable. However, the presentinvention is not limited to this structure. The switching TFT and the ELdriver TFT may be either n-channel TFTs or p-channel TFTs.

[0215] The switching TFT 8201 has an active layer containing a sourceregion 813, a drain region 814, LDD regions 815 a to 815 d, a separationregion 816, and an active layer including channel forming regions 863and 864, a gate insulating film 818, gate electrodes 819 a and 819 b, afirst interlayer insulating film 820, a source signal line 821 and adrain wiring 822. Note that the gate insulating film 818 and the firstinterlayer insulating film 820 may be common among all TFTs on thesubstrate, or may differ depending upon the circuit or the element. Inaddition, the reference numeral 817 a and 817 b are masks to form thechannel forming region.

[0216] Furthermore, the switching TFT 8201 shown in FIG. 18 iselectrically connected to the gate electrodes 819 a and 819 b, becomingnamely a double gate structure. Not only the double gate structure, butalso a multi-gate structure (a structure containing an active layerhaving two or more channel forming regions connected in series) such asa triple gate structure, may of course also be used.

[0217] The multi-gate structure is extremely effective in reducing theoff current, and provided that the off current of the switching TFT issufficiently lowered, a capacitor connected to the gate electrode of thefirst EL driver TFT 8202 can be have its capacitance reduced to theminimum necessary. Namely, the surface area of the capacitor can be madesmaller, and therefore using the multi-gate structure is also effectivein expanding the effective light emitting surface area of the ELelements.

[0218] In addition, the LDD regions 815 a to 815 d are formed so as notto overlap the gate electrodes 819 a and 819 b through the gateinsulating film 818 in the switching TFT 8201. This type of structure isextremely effective in reducing the off current. Furthermore, the length(width) of the LDD regions 815 a to 815 d may be set from 0.5 to 3.5 μm,typically between 2.0 and 2.5 μm.

[0219] Note that forming an offset region (a region which is asemiconductor layer having the same composition as the channel formingregion and to which the gate voltage is not applied) between the channelforming region and the LDD region is additionally preferable in that theoff current is lowered. Further, when using a multi-gate structurehaving two or more gate electrodes, the separation region 816 (a regionto which the same impurity element, at the same concentration, as thatadded to the source region or the drain region, is added) is effectivein reducing the off current.

[0220] Next, the first EL driver TFT 8202 is formed having an activelayer containing a source region 826, a drain region 827, and a channelforming region 805; the gate insulating fihn 818; a gate electrode 830,the first interlayer insulating film 820; a source wiring 831; and adrain wiring 832. The first EL driver TFT 8202 is a p-channel TFT inEmbodiment 11. The reference numeral 829 is a mask to form the channelforming region.

[0221] Further, the drain region 814 of the switching TFT 8201 isconnected to the gate electrode 830 of the EL driver TFT 8202. Althoughnot shown in the figure, specifically the gate electrode 830 of the ELdriver TFT 8202 is electrically connected to the drain region 814 of theswitching TFT 8201 through the drain wiring (also referred to as aconnection wiring) 822. The source wiring 831 of the first EL driver TFT8202 is connected to an power source supply line (not shown in thefigure).

[0222] The first EL driver TFT 8202 is an element for controlling theamount of electric current injected to the EL element, and a relativelylarge amount of current flows. It is therefore preferable to design thechannel width W to be larger than the channel width of the switchingTFT. Further, it is preferable to design the channel length L such thatan excess of electric current does not flow in the EL driver TFT 8202.It is preferable to have from 0.5 to 2 μA (more preferably between 1 and1.5 μA) per pixel.

[0223] In addition, by making the film thickness of the active layers(particularly the channel forming region) of the EL driver TFT 8202thicker (preferably from 50 to 100 nm. even is better between 60 and 80nm), deterioration of the TFT may be suppressed. Conversely, it is alsoeffective to make the film thickness of the active layer (particularlythe channel forming region) thinner (preferably from 20 to 50 nm, evenbetter between 25 and 40 nm), from the standpoint of making the offcurrent smaller, for the case of the switching TFT 8201.

[0224] The structures of the TFTs formed within the pixel are explainedabove, but a driver circuit is also formed simultaneously at this point.A CMOS circuit which becomes a basic unit for forming the driver circuitis shown in FIG. 18.

[0225] A TFT having a structure in which hot carrier injection isreduced without an excessive drop in the operating speed is used as ann-channel TFT 8204 of the CMOS circuit in FIG. 18. Note that the termdriver circuit indicates a source signal line driver circuit and a gatesignal line driver circuit here. It is also possible to form other logiccircuit (such as a level shifter, an A/D converter, and a signaldivision circuit).

[0226] An active layer of the n-channel TFT 8204 of the CMOS circuitcontains a source region 835, a drain region 836, an LDD region 837, anda channel forming region 862. The LDD region 837 overlaps with a gateelectrode 839 through the gate insulating film 818. Therefore, the LDDregion 837 is made to overlap with the gate electrode completely. It ispreferable to reduce the resistance component as much as possible. Thereference numeral 838 is a mask to form the channel formation region.

[0227] Formation of the LDD region 837 on only the drain region 836 sideis so as not to have drop the operating speed. Further,it is notnecessary to be very concerned about the off current with the n-channelTFT 8204, and it is good to place more importance on the operatingspeed. Thus, it is desirable that the LDD region 837 is made tocompletely overlap the gate electrode to decrease a resistance componentto a minimum. It is therefore preferable to eliminate so-called offset.

[0228] Furthermore, there is almost no need to be concerned withdegradation of a p-channel TFT 8205 of the CMOS circuit, due to hotcarrier injection, and therefore no LDD region need be formed inparticular. Its active layer therefore contains a source region 840, adrain region 841, and a channel forming region 861, and a gateinsulating film 818 and a gate electrode 843 are formed on the activelayer. It is also possible, of course, to take measures against hotcarrier injection by forming an LDD region similar to that of then-channel TFT 8204. The reference numeral 842 is a mask to form thechannel formation region.

[0229] Further, the n-channel TFT 8204 and the p-channel TFT 8205 havesource wirings 844 and 845 respectively, on their source regions,through the first interlayer insulating film 820. In addition, the drainregions of the n-channel TFT 8204 and the p-channel TFT 8205 aremutually connected electrically by a drain wiring 846.

[0230] Next, reference numeral 847 denotes a first passivation film, andits film thickness may be set from 10 nm to 1 μm (preferably between 200and 500 nm). An insulating film containing silicon (in particular, it ispreferable to use an oxidized silicon nitride film or a silicon nitridefilm) can be used as the passivation film material. The passivation film847 possesses a role of protecting the TFTs from alkaline metals andmoisture. Alkaline metals such as sodium are contained in an EL layerformed last on the final TFT (in particular, the EL driver TFT). Inother words, the first passivation film 847 works as a protecting layerso that these alkaline metals (mobile ions) do not penetrate into theTFT.

[0231] Further, reference numeral 848 denotes a second interlayerinsulating film, which has a function as a leveling film for performingleveling of a step due to the TFTs. An organic resin film is preferableas the second interlayer insulating film 848, and one such as polyimide,polyamide, acrylic, or BCB (benzocyclobutene) may be used. These organicresin films have the advantages of easily forming a good, level surface,having a low specific dielectric constant. The EL layer is extremelysensitive to unevenness, and therefore it is preferable to mostly absorbthe TFT step by the second interlayer insulating film 848. In addition,it is preferable to form the low specific dielectric constant materialthickly in order to reduce the parasitic capacitance formed between thegate signal wiring, the data signal wiring and the cathode of the ELelement. The thickness, therefore, is preferably from 0.5 to 5 μm (morepreferably between 1.5 and 2.5 μm).

[0232] Further, reference numeral 849 denotes a pixel electrode (ELelement anode) made from a transparent conducting film. After forming acontact hole (opening) in the second interlayer insulating film 848 andin the first passivation film 847, the pixel electrode 849 is formed soas to be connected to the drain wiring 832 of the first EL driver TFT8202. Note that if the pixel electrode 849 and the drain region 827 areformed so as not to be directly connected, as in FIG. 18, then alkalinemetals of the EL layer can be prevented from entering the active layervia the pixel electrode.

[0233] A third interlayer insulating film 850 is formed on the pixelelectrode 849 from a silicon oxide film, a silicon oxynitride film, oran organic resin film, with a thickness of from 0.3 to 1 μm. An openportion is formed in the third interlayer insulating film 850 over thepixel electrode 849 by etching, and the edge of the open portion isetched so as to become a tapered shape. The taper angle may be set from10 to 60°, (preferably between 30 and 50°).

[0234] An EL layer 851 is formed on the third interlayer insulating film850. A single layer structure or a lamination structure can be used forthe EL layer 851, but the lamination structure has a better lightemitting efficiency. In general, a hole injecting layer, a holetransporting layer, a light emitting layer, and an electron transportinglayer are formed in order on the pixel electrode, but a structure havinga hole transporting layer, a light emitting layer, and an electrontransporting layer, or a structure having a hole injecting layer, a holetransporting layer, a light emitting layer, an electron transportinglayer, and an electron injecting layer may also be used. Any knownstructure may be used by the present invention, and doping of such as afluorescing pigment into the EL layer may also be performed.

[0235] The structure of FIG. 18 is an example of a case of forming threetypes of EL elements corresponding to R, G, and B. Note that althoughonly one pixel is shown in FIG. 18, pixels having an identical structureare formed corresponding to red, green and blue colors, respectively,and that color display can thus be performed. It is possible toimplement the present invention without concern as to the method ofcolor display.

[0236] A cathode 852 of the EL element is formed on the EL layer 851 asa counter electrode. A material containing a low work coefficientmaterial such as magnesium (Mg), lithium (Li). or calcium (Ca), is usedas the cathode 852. Preferably, an electrode made from MgAg (a materialmade from Mg and Ag at a mixture of Mg:Ag=10:1) is used. In addition, aMgAgAl electrode, an LiAl electrode, and an LiFAl electrode can be givenas other examples.

[0237] The lamination body comprising the EL layer 851 must be formedseparately for each pixel, but the EL layer 851 is extremely weak withrespect to moisture, and consequently a normal photolithographytechnique cannot be used. It is therefore preferable to use a physicalmask material such as a metal mask, and to selectively form the layersby a gas phase method such as vacuum evaporation, sputtering, or plasmaCVD.

[0238] The EL element 8206 is formed by the pixel electrode (anode) 849,the EL layer 851 and the cathode 852.

[0239] Note that it is also possible to use a method such as ink jetprinting, screen printing or spin coating as the method of selectivelyforming the EL layer. However, the cathode cannot be formed insuccession with these methods at present, and therefore it is preferableto use the other methods stated above.

[0240] Further, reference numeral 853 denotes a protecting electrode,which protects the EL layer and the cathode 852 from external moistureand the like at the same time is an electrode for connecting to thecathode 852 of each pixel. It is preferable to use a low resistancematerial containing aluminum (Al), copper (Cu), or silver (Ag) as theprotecting electrode 853. The protecting electrode 853 can also beexpected to have a heat radiating effect which relieves the amount ofheat generated by the EL layer.

[0241] Reference numeral 854 denotes a second passivation film, whichmay be formed with a film thickness of 10 nm to 1 μm (preferably between200 and 500 nm). The aim of forming the second passivation film 854 ismainly for protecting the EL layer 851 from moisture. but it is alsoeffective to give the second passivation film 854 a heat radiatingeffect. Note that the EL layer is weak with respect to heat, as statedabove, and therefore it is preferable to perform film formation at aslow a temperature as possible (preferably within a temperature rangefrom room temperature to 120° C.). Plasma CVD, sputtering, vacuumevaporation, ion plating, and solution coating (spin coating) cantherefore be considered as preferable film formation methods.

[0242] Note that it goes without saying that all of the TFTs shown inFIG. 18 may have a polysilicon film as their active layer in the presentinvention.

[0243] When the pinhole is formed in the EL layer 860 in the lightemitting device, the defective portion that the pixel electrode 849 andthe cathode 852 are connecting through the pinhole is formed. By therepair method of the present invention, resistance can be higher bychanging the defective portion to the denatured portion 860. Therefore,the brightness in the portion other than the pinhole of the pixel areraised, and the deterioration of the EL layer surrounding of the pinholecan be prevented the promotion.

[0244] Note that it is possible to implement Embodiment 11 combinationwith Embodiments 1 to 4, 6 and 8.

[0245] [Embodiment 12]

[0246] A light emitting device using an EL element is self-luminous andtherefore is superior in visibility in bright surroundings compared toliquid crystal display devices and has wider viewing angle. Accordingly,it can be used for display units of various electric equipment.

[0247] Given as examples of electric equipment employing a lightemitting device to which a repairing method of the present invention isapplied are: a video camera; a digital camera; a goggle type display(head mounted display); a navigation system; an audio reproducing device(car audio, an audio component, and the like); a notebook computer; agame machine; a portable information terminal (a mobile computer, acellular phone, a portable game machine, an electronic book, etc.); andan image reproducing device (specifically, a device capable ofprocessing data in a recording medium such as a digital versatile disk(DVD) and having a display device that can display the image of thedata). The light emitting device having an EL element is desirableparticularly for a portable information terminal since its screen isoften viewed obliquely and is required to have a wide viewing angle.Specific examples of the electric equipment are shown in FIGS. 11A to11H.

[0248]FIG. 11A shows an EL display device, which comprises a casing2001, a supporting base 2002, a display unit 2003, speaker units 2004, avideo input terminal 2005, etc. The light emitting device to which therepairing method of the present invention is applied can be used for thedisplay unit 2003. The light emitting device having an EL element isself-luminous and does not need a backlight, so that it can make athinner display unit than liquid display devices can. The term ELdisplay device includes every display device for displaying informationsuch as one for a personal computer, one for receiving TV broadcasting,and one for advertisement.

[0249]FIG. 11B shows a digital still camera, which comprises a main body2101, a display unit 2102, an image receiving unit 2103, operation keys2104. an external connection port 2105, a shutter 2106, etc. The lightemitting device to which the repairing method of the present inventionis applied can be used for the display unit 2102.

[0250]FIG. 11C shows a notebook computer, which comprises a main body2201, a casing 2202, a display unit 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, etc. The light emittingdevice to which the repairing method of the present invention is appliedcan be used for the display unit 2203.

[0251]FIG. 11D shows a mobile computer, which comprises a main body2301, a display unit 2302, a switch 2303, operation keys 2304, aninfrared ray port 2305, etc. The light emitting device to which therepairing method of the present invention is applied can be used for thedisplay unit 2302.

[0252]FIG. 11E shows a portable image reproducing device equipped with arecording medium (a DVD player, to be specific). The device comprises amain body 2401, a casing 2402, a display unit A 2403, a display unit B2404, a recording medium (DVD) reading unit 2405, operation keys 2406,speaker units 2407, etc. The display unit A 2403 mainly displays imageinformation whereas the display unit B 2404 mainly displays textinformation. The light emitting device to which the repairing method ofthe present invention is applied can be used for the display units A2403 and B 2404. The term image reproducing device equipped with arecording medium includes video game machines.

[0253]FIG. 11F shows a goggle type display (head mounted display), whichcomprises a main body 2501, display units 2502, and arm units 2503. Thelight emitting device to which the repairing method of the presentinvention is applied can be used for the display units 2502.

[0254]FIG. 11G shows a video camera, which comprises a main body 2601, adisplay unit 2602, a casing 2603, an external connection port 2604, aremote control receiving unit 2605, an image receiving unit 2606, abattery 2607, an audio input unit 2608, operation keys 2609, etc. Thelight emitting device to which the repairing method of the presentinvention is applied can be used for the display unit 2602.

[0255]FIG. 11H shows a cellular phone, which comprises a main body 2701,a casing 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The light emitting device to which the repairingmethod of the present invention is applied can be used for the displayunit 2703. If the display unit 2703 displays white characters on a blackbackground, power consumption of the cellular phone can be reduced.

[0256] If the luminance of light emitted from EL materials is increasedin future, the light emitting device having an EL element can be usedalso in a front or rear projector in which light bearing outputted imageinformation is magnified by a lens or the like to be projected on ascreen.

[0257] The electric equipment given in the above often displaysinformation distributed through electronic communication lines such asInternet and CATV (cable television), especially, animation informationwith increasing frequency. The light emitting device having an ELelement is suitable for displaying animation information since ELmaterials have fast response speed.

[0258] In the light emitting device, portions that emit light consumepower. Therefore it is desirable to display information such that assmall portions as possible emit light. Accordingly, if the lightemitting device is used for a display unit that mainly displays textinformation such as a portable information terminal, in particular, acellular phone, and an audio reproducing device, it is desirable toassign light emitting portions to display text information whileportions that do not emit light serve as the background.

[0259] As described above, the application range of the light emittingdevice to which the present invention is applied is very wide andelectric equipment of every field can employ the device. The electricequipment in this embodiment may use any of the structures shown inEmbodiments 1 through 11.

[0260] [Embodiment 13]

[0261] This embodiment describes a case of applying a repairing methodof the present invention to a passive (simple) matrix light emittingdevice.

[0262]FIG. 19A shows the structure of a passive matrix light emittingdevice. Reference numeral 805 denotes a pixel portion, which has aplurality of pixels 806. Each pixel has one of plural data lines 803 andone of plural scanning lines 804. EL layers are formed between the datalines 803 and the scanning lines 804. The data lines 803 and thescanning lines 804 serve as electrodes. The EL layers and the electrodesconstitute EL elements 807.

[0263] Signals to be inputted to the data lines 803 are controlled by adata line driving circuit 801, and signals to be inputted to thescanning lines 804 are controlled by a scanning line driving circuit802.

[0264]FIG. 19B shows the voltage level of signals inputted to thescanning lines 804 and the data lines 803 when the repairing method ofthe present invention is applied. By changing the voltage of the datalines at given time intervals while keeping the voltage of the scanninglines 804 constant, a reverse bias current is caused to flow into the ELelements 807 at given time intervals.

[0265] The defect portions of the EL elements 807 may be repaired atonce in all of the pixels 805 of the pixel portion 806. Alternatively,the repair may be performed on one line of pixels at a time, or on onepixel at a time.

[0266] The method of the present invention can increase the amount ofcurrent actually flowing through the EL layer upon application of aforward bias voltage to the EL element even if a pin hole is formed inthe EL layer during formation of the layer due to dusts or the like andtwo layers sandwiching a light emitting layer short-circuit, because themethod can raise the resistance of the defect portion where the shortcircuit takes place by changing the defect portion into the transmutedportion. Therefore the repairing method of the present invention canraise the luminance of emitted light with application of the same levelof voltage despite the presence of the defect portion.

[0267] Having high resistance R_(SC), the transmuted portion hardlyallows a current to flow therein in contrast to the defect portion wherethere is always a flow of current to accelerate degradation of a part ofthe EL layer that surrounds the defect portion. Therefore, degradationis not accelerated in a part of the EL layer that surrounds thetransmuted portion.

[0268] This embodiment may be combined freely with Embodiments 5 through8, and Embodiment 12.

[0269] With the above structures, the method of the present inventioncan increase the amount of current actually flowing through the EL layerupon application of a forward bias voltage to the EL element even if apin hole is formed in the EL layer during formation of the layer due todusts or the like and two layers sandwiching a light emitting layershort-circuit, because the method can raise the resistance of the defectportion where the short circuit takes place by changing the defectportion into the transmuted portion. Therefore the repairing method ofthe present invention can raise the luminance of emitted light withapplication of the same level of voltage despite the presence of thedefect portion.

[0270] Having high resistance R_(SC), the transmuted portion hardlyallows a current to flow therein in contrast to the defect portion wherethere is always a flow of current to accelerate degradation of a part ofthe EL layer that surrounds the defect portion. Therefore, degradationis not accelerated in a part of the EL layer that surrounds thetransmuted portion.

What is claimed is:
 1. A method of repairing a light emitting devicecomprising a step of applying a first voltage and a second voltage to alight emitting element in order, wherein the first voltage and thesecond voltage are reverse bias voltages of different levels.
 2. Amethod according to claim 1, wherein the first voltage and the secondvoltage are within ±15% of an avalanche voltage of the light emittingelement.
 3. A method according to claim 1, wherein the light emittingelement is an electroluminescence element.
 4. A method according toclaim 1, wherein the light emitting device is included in an electricdevice selected from the group consisting of a video camera, a digitalcamera, a goggle type display, a head mounted display, a navigationsystem, an audio reproducing device, a car audio, an audio component, anotebook computer, a game machine a portable information terminal, amobile computer, a cellular phone, a portable game machine, anelectronic book, an image reproducing device, and a digital versatiledisk (DVD) player.
 5. A method of repairing a light emitting devicecomprising a step of gradually changing a voltage applied to a lightemitting element from a first voltage to a second voltage, wherein thefirst voltage and the second voltage are reverse bias voltages ofdifferent levels.
 6. A method according to claim 5, wherein the firstvoltage and the second voltage are within ±15% of an avalanche voltageof the light emitting element.
 7. A method according to claim 5, whereinthe light emitting element is an electroluminescence element.
 8. Amethod according to claim 5, wherein the light emitting device isincluded in an electric device selected from the group consisting of avideo camera, a digital camera, a goggle type display, a head mounteddisplay, a navigation system, an audio reproducing device, a car audio,an audio component, a notebook computer, a game machine, a portableinformation terminal, a mobile computer, a cellular phone, a portablegame machine, an electronic book, an image reproducing device, and adigital versatile disk (DVD) player.
 9. A method of repairing a lightemitting device comprising a step of: applying a first voltage and asecond voltage in order between an anode and a cathode of the lightemitting device, wherein the anode and the cathode are located in alight emitting element with a light emitting layer interposedtherebetween, and wherein the first voltage and the second voltage arereverse bias voltages of different levels.
 10. A method according toclaim 9, wherein the first voltage and the second voltage are within±15% of an avalanche voltage of the light emitting element.
 11. A methodaccording to claim 9, wherein the light emitting element is anelectroluminescence element.
 12. A method according to claim 9, whereinthe light emitting device is included in an electric device selectedfrom the group consisting of a video camera, a digital camera, a goggletype display, a head mounted display, a navigation system, an audioreproducing device, a car audio, an audio component, a notebookcomputer, a game machine, a portable information terminal, a mobilecomputer, a cellular phone, a portable game machine, an electronic book,an image reproducing device, and a digital versatile disk (DVD) player.13. A method of repairing a light emitting device comprising a step of:gradually changing a voltage applied between an anode and an cathode ofthe light emitting device from a first voltage to a second voltage,wherein the anode and the cathode are located in a light emittingelement with a light emitting layer interposed therebetween, and whereinthe first voltage and the second voltage are reverse bias voltages ofdifferent levels.
 14. A method according to claim 13, wherein the firstvoltage and the second voltage are within ±15% of an avalanche voltageof the light emitting element.
 15. A method according to claim 13,wherein the light emitting element is an electroluminescence element.16. A method according to claim 13, wherein the light emitting device isincluded in an electric device selected from the group consisting of avideo camera, a digital camera, a goggle type display, a head mounteddisplay, a navigation system, an audio reproducing device, a car audio,an audio component, a notebook computer, a game machine, a portableinformation terminal, a mobile computer, a cellular phone, a portablegame machine, an electronic book, an image reproducing device, and adigital versatile disk (DVD) player.
 17. A method of repairing a lightemitting device comprising a step of: applying a first voltage and asecond voltage in order between an anode and a cathode of the lightemitting device, thereby making a portion where a reverse-bias currentflows between the anode and the cathode insulating or highly resistive,and wherein the anode and the cathode are located in a light emittingelement with a light emitting layer interposed therebetween, and whereinthe first voltage and the second voltage are reverse bias voltages ofdifferent levels.
 18. A method according to claim 17, wherein the firstvoltage and the second voltage are within ±15% of an avalanche voltageof the light emitting element.
 19. A method according to claim 17,wherein the light emitting element is an electroluminescence element.20. A method according to claim 17, wherein the light emitting device isincluded in an electric device selected from the group consisting of avideo camera, a digital camera, a goggle type display, a head mounteddisplay, a navigation system, an audio reproducing device, a car audio,an audio component, a notebook computer, a game machine, a portableinformation terminal, a mobile computer, a cellular phone, a portablegame machine, an electronic book, an image reproducing device, and adigital versatile disk (DVD) player.
 21. A method of repairing a lightemitting device comprising a step of: gradually changing a voltageapplied between an anode and an cathode of the light emitting devicefrom a first voltage to a second voltage, thereby making a portion wherea reverse-bias current flows between the anode and the cathodeinsulating or highly resistive, wherein the anode and the cathode arelocated in a light emitting element with a light emitting layerinterposed therebetween, and wherein the first voltage and the secondvoltage are reverse bias voltages of is different levels.
 22. A methodaccording to claim 21, wherein the first voltage and the second voltageare within ±15% of an avalanche voltage of the light emitting element.23. A method according to claim 21, wherein the light emitting elementis an electroluminescence element.
 24. A method according to claim 21,wherein the light emitting device is included in an electric deviceselected from the group consisting of a video camera, a digital camera,a goggle type display, a head mounted display, a navigation system, anaudio reproducing device, a car audio, an audio component, a notebookcomputer, a game machine, a portable information terminal, a mobilecomputer, a cellular phone, a portable game machine, an electronic book,an image reproducing device, and a digital versatile disk (DVD) player.25. A method of repairing a light emitting device comprising a step ofapplying a first voltage and a second voltage to a light emittingelement in order, wherein the first voltage is a ground voltage whilethe second voltage is a reverse bias voltage.
 26. A method according toclaim 25, wherein the reverse bias voltage is within ±15% of anavalanche voltage of the light emitting element.
 27. A method accordingto claim 25, wherein the light emitting element is anelectroluminescence element.
 28. A method according to claim 25, whereinthe light emitting device is included in an electric device selectedfrom the group consisting of a video camera, a digital camera, a goggletype display, a head mounted display, a navigation system, an audioreproducing device, a car audio, an audio component, a notebookcomputer, a game machine, a portable information terminal, a mobilecomputer, a cellular phone, a portable game machine, an electronic book,an image reproducing device, and a digital versatile disk (DVD) player.29. A method of repairing a light emitting device comprising a step ofgradually changing a voltage applied to a light emitting element from afirst voltage to a second voltage, wherein one of the first voltage andthe second voltage is a ground voltage while the other is a reverse biasvoltage.
 30. A method according to claim 29, wherein the reverse biasvoltage is within ±15% of an avalanche voltage of the light emittingelement.
 31. A method according to claim 29, wherein the light emittingelement is an electroluminescence element.
 32. A method according toclaim 29, wherein the light emitting device is included in an electricdevice selected from the group consisting of a video camera, a digitalcamera, a goggle type display, a head mounted display, a navigationsystem, an audio reproducing device, a car audio, an audio component, anotebook computer, a game machine, a portable information terminal, amobile computer, a cellular phone, a portable game machine, anelectronic book, an image reproducing device, and a digital versatiledisk (DVD) player.
 33. A method of repairing a light emitting devicecomprising a step of: applying a first voltage and a second voltage inorder between an anode and a cathode of the light emitting device,wherein the anode and the cathode are located in a light emittingelement with a light emitting layer interposed therebetween, and whereinthe first voltage is a ground voltage while the second voltage is areverse bias voltage.
 34. A method according to claim 33, wherein thereverse bias voltage is within ±15% of an avalanche voltage of the lightemitting element.
 35. A method according to claim 33, wherein the lightemitting element is an electroluminescence element.
 36. A methodaccording to claim 33, wherein the light emitting device is included inan electric device selected from the group consisting of a video camera,a digital camera, a goggle type display, a head mounted display, anavigation system, an audio reproducing device, a car audio, an audiocomponent, a notebook computer, a game machine, a portable informationterminal, a mobile computer, a cellular phone, a portable is gamemachine, an electronic book, an image reproducing device, and a digitalversatile disk (DVD) player.
 37. A method of repairing a light emittingdevice comprising a step of: gradually changing a voltage appliedbetween an anode and an cathode of the light emitting device from afirst voltage to a second voltage, wherein the anode and the cathode arelocated in a light emitting element with a light emitting layerinterposed therebetween, and wherein one of the first voltage and thesecond voltage is a ground voltage while the other is a reverse biasvoltage.
 38. A method according to claim 37, wherein the reverse biasvoltage is within ±15% of an avalanche voltage of the light emittingelement.
 39. A method according to claim 37, wherein the light emittingelement is an electroluminescence element.
 40. A method according toclaim 37, wherein the light emitting device is included in an electricdevice selected from the group consisting of a video camera, a digitalcamera, a goggle type display, a head mounted display, a navigationsystem, an audio reproducing device, a car audio, an audio component, anotebook computer, a game machine, a portable information terminal, amobile computer, a cellular phone, a portable game machine, anelectronic book, an image reproducing device, and a digital versatiledisk (DVD) player.
 41. A method of repairing a light emitting devicecomprising a step of: applying a first voltage and a second voltage inorder between an anode and a cathode of the light emitting device,thereby making a portion where a reverse-bias current flows between theanode and the cathode insulating or highly resistive, and wherein theanode and the cathode are located in a light emitting element with alight emitting layer interposed therebetween, and wherein the firstvoltage is a ground voltage while the second voltage is a reverse biasvoltage.
 42. A method according to claim 41, wherein the reverse biasvoltage is within ±15% of an avalanche voltage of the light emittingelement.
 43. A method according to claim 41, wherein the light emittingelement is an electroluminescence element.
 44. A method according toclaim 41, wherein the light emitting device is included in an electricdevice selected from the group consisting of a video camera, a digitalcamera, a goggle type display, a head mounted display, a navigationsystem, an audio reproducing device, a car audio, an audio component, anotebook computer, a game machine, a portable information terminal, amobile computer, a cellular phone, a portable game machine, anelectronic book, an image reproducing device, and a digital versatiledisk (DVD) player.
 45. A method of repairing a light emitting devicecomprising a step of: gradually changing a voltage applied between ananode and an cathode of the light emitting device from a first voltageto a second voltage, thereby making a portion where a reverse-biascurrent flows between the anode and the cathode insulating or highlyresistive, wherein the anode and the cathode are located in a lightemitting element with a light emitting layer interposed therebetween,and wherein one of the first voltage and the second voltage is a groundvoltage while the other is a reverse bias voltage.
 46. A methodaccording to claim 45, wherein the reverse bias voltage is within ±15%of an avalanche voltage of the light emitting element.
 47. A methodaccording to claim 45, wherein the light emitting element is anelectroluminescence element.
 48. A method according to claim 45, whereinthe light emitting device is included in an electric device selectedfrom the group consisting of a video camera, a digital camera, a goggletype display, a head mounted display, a navigation system, an audioreproducing device, a car audio, an audio component, a notebookcomputer, a game machine, a portable information terminal, a mobilecomputer, a cellular phone, a portable game machine, an electronic book,an image reproducing device, and a digital versatile disk (DVD) player.49. A method of fabricating a light emitting device comprising a stepof: forming a light emitting element comprising an anode and a cathodewith a light emitting layer interposed therebetween; and applying afirst voltage and a second voltage in order between an anode and acathode of the light emitting device, thereby making a portion where areverse-bias current flows between the anode and the cathode insulatingor highly resistive, wherein the first voltage and the second voltageare reverse bias voltages of different levels.
 50. A method according toclaim 49, wherein the first voltage is gradually changed to the secondvoltage,
 51. A method according to claim 49, wherein the first voltageand the second voltage are within ±15% of an avalanche voltage of thelight emitting element.
 52. A method according to claim 49, wherein thelight emitting element is an electroluminescence element.
 53. A methodaccording to claim 49, wherein the light emitting device is included inan electric device selected from the group consisting of a video camera,a digital camera, a goggle type display, a head mounted display, anavigation system, an audio reproducing device, a car audio, an audiocomponent, a notebook computer, a game machine, a portable informationterminal, a mobile computer, a cellular phone, a portable game machine,an electronic book, an image reproducing device, and a digital versatiledisk (DVD) player.
 54. A method of fabricating a light emitting devicecomprising a step of: forming a light emitting element comprising ananode and a cathode with a light emitting layer interposed therebetween;and applying a first voltage and a second voltage in order between ananode and a cathode of the light emitting device, thereby making aportion where a reverse-bias current flows between the anode and thecathode insulating or highly resistive, wherein the first voltage is aground voltage while the second voltage is a reverse bias voltage.
 55. Amethod according to claim 54, wherein the first voltage is graduallychanged to the second voltage,
 56. A method according to claim 54,wherein the first voltage and the second voltage are within ±15% of anavalanche voltage of the light emitting element.
 57. A method accordingto claim 54, wherein the light emitting element is anelectroluminescence element.
 58. A method according to claim 54, whereinthe light emitting device is included in an electric device selectedfrom the group consisting of a video camera, a digital camera, a goggletype display, a head mounted display, a navigation system, an audioreproducing device, a car audio, an audio component, a notebookcomputer, a game machine, a portable information terminal, a mobilecomputer, a cellular phone, a portable game machine, an electronic book,an image reproducing device, and a digital versatile disk (DVD) player.